Wireless communication device

1. A wireless communication device comprising: a wireless IC device; a multilayer substrate defined by a multilayer body including a plurality of dielectric layers; a resonant circuit connected to the wireless IC device, the resonant circuit including: an inductance element; and a capacitance element provided in the multilayer substrate; and a radiation conductor connected to the resonant circuit; wherein the capacitance element includes: first and second electrode patterns located on at least one layer of the plurality of dielectric layers; and third and fourth electrode patterns that are located on at least another layer of the plurality of dielectric layers and that are opposite the first and second electrode patterns; the first and fourth electrode patterns have an identical potential, and the second and third electrode patterns have an identical potential; and in plan view in a stacking direction of the plurality of dielectric layers, an outline of one of the first and third electrode patterns is present inside an outline of the other, and an outline of one of the second and fourth electrode patterns is present inside an outline of the other.

2. The wireless communication device according to claim 1 , wherein the multilayer substrate includes first and second external electrodes on a back surface opposite a principal surface, the first and second external electrodes being arranged to connect the multilayer substrate to a printed circuit board; the capacitance element includes first and second electrode patterns located on at least one layer of the plurality of dielectric layers, the first and second electrode patterns being opposite to the first and second external electrodes in the stacking direction of the plurality of dielectric layers; and in plan view in the stacking direction, the first electrode pattern has the same or substantially the same outline dimensions as outline dimensions of the first external electrode, and the second electrode pattern has the same or substantially the same outline dimensions as outline dimensions of the second external electrode.

3. The wireless communication device according to claim 1 , wherein the inductance element includes a loop defined by at least a portion of the radiation conductor.

4. The wireless communication device according to claim 1 , wherein the wireless IC device inputs/outputs a high frequency signal obtained by modulating a carrier by using information, and a resonant frequency of the resonant circuit is equal or substantially equal to a frequency of the carrier.

5. The wireless communication device according to claim 1 , wherein an inductance element constituted by a coil pattern that defines the resonant circuit is not provided in the multilayer substrate.

6. The wireless communication device according to claim 1 , wherein the wireless IC device is mounted on a principal surface of the multilayer substrate.

7. The wireless communication device according to claim 2 , wherein the radiation conductor defines a ground conductor located on/in the printed circuit board.

8. The wireless communication device according to claim 1 , wherein the wireless communication device is an RFID tag or a reader/writer device.

9. The wireless communication device according to claim 1 , wherein the radiation conductor is defined by a ground electrode or a metal case of the wireless communication device.